Cigarette smoking is a major independent risk factor for cardiovascular disease. Among over 4,000 chemicals in tobacco smoking, nicotine, the primary addictive agent in cigarettes, is one of the major component of tobacco smoke. Nicotine is also the major constituent in electronic cigarettes (EC) - which are becoming popular as an alternative to smoking tobacco. Although there is overwhelming epidemiological evidence linking smoking, nicotine, and cardiovascular diseases, there is no direct evidence showing that nicotine instigates atherosclerotic plaque instability (so called rupture). A causative link of smoking and plaque instability remains to be established. We have obtained exciting preliminary data demonstrating that infusion of smokers-relevant concentrations of nicotine promoted atherosclerotic plaque instability in our well-characterized mouse models in vivo. Nicotine not only dramatically elevated serum level interleukin 1 (IL-1)? but also obviously upregulated NALP3 inflammasome complex components and IL-1? in advanced atherosclerotic plaques. In addition, the inhibition of caspase 1, a key downstream target of NLRP3 inflammasome complex, restrained nicotine- stimulated atherosclerotic plaque formation and plaque rapture. Thus, the central hypothesis of this application is that nicotine in smoking promotes atherosclerotic plaque rapture by activating inflammasome in vascular smooth muscle cell (VSMC). To validate or refute this hypothesis, we propose three aims: Aim 1 is to evaluate and compare the impacts of nicotine alone and electronic cigarettes exposure on atherosclerotic plaque instability and IL-1? levels in our well-characterized mouse models in vivo and in autopsy samples of human smokers and non-smokers. Aim 2 is to define the contributions of NLRP3 inflammasome activation and IL-1? in nicotine- and electronic cigarettes - induced atherosclerotic plaque instability, identify whether IL-1? is a trigger for plaque instability in smokers. In this aim, we will examine the role of NLRP3 inflammasome in regulating nicotine- or EC- induced plaque instability by using NLRP3-/-Apoe-/-, ASC-/-Apoe-/-, Caspase1-/-Apoe-/- mice. We will also perform administration of IL-1? neutralizing antibody in vivo to study whether blocking of IL-1? will reverse nicotine- and electronic cigarettes-induced plaque instability. Finally, VSMC-specific NLRP3 knockout mice in Apoe-/- background will be generated and challenged with nicotine and electronic cigarettes to study the contribution of VSMC-derived NLRP3 inflammasome activation in nicotine- and electronic cigarettes-induced atherosclerotic plaque instability. Aim 3 is to determine how nicotine activates NLRP3 inflammasome in VSMC. The completion of this study will unveil the molecular insights by which nicotine effect on atherosclerotic plaque instability, and identify IL-1? as a novel therapeutic target for nicotine- or electronic cigarettes-induced plaque instability.